1. Field of the Invention
The present invention relates to a single-phase brushless motor in which a salient pole of a stator has a specific structure.
2. Related Art
A structure of a salient pole of a stator core in an outer-rotor-type single-phase brushless motor, in which at both end portions in a rotation direction, a gap width is continuously varied in a rotation direction, so that a gap between a rotor and one end portion is made minimum and a gap between the rotor and the other end portion is made maximum, is disclosed in Japanese Patent Application Laid-Open No. 2006-333585.
In the single-phase brushless motor, there is a problem in which both superior start-up stability and low cogging torque are required. The start-up stability means a characteristic in which stable start occurs when electrifying is started from a stopped state. In order to obtain the start-up stability, it is effective that a tip shape of the salient pole of the stator core described in Japanese Patent Application Laid-Open No. 2006-333585 be formed so as to be asymmetrical in a circumferential direction. However, although the above structure described in Japanese Patent Application Laid-Open No. 2006-333585 is effective for increasing the start-up stability, there is a problem in that the cogging torque is increased. The cogging torque is nonuniformity in running torque, and it causes vibration or noise in the rotating of the motor.
Under these circumstances, an object of the present invention is to provide a single-phase brushless motor having both superior start-up stability and low cogging torque.